Films containing two or more metals are generally known in the art, and may be referred to as multi-metallic films. A multi-metallic film may be formed from an alloy of two or more metals, and/or from one or more metal compounds, where a metal compound itself may contain more than one metal. Typical metal compounds are metal borides, nitrides, oxides and sulfides. Multi-metallic films find use in the semiconductor industry, and have been proposed for various special applications. For example, a Ti.sub.1-x Al.sub.x N.sub.2 thin film has been proposed as a useful barrier layer which may be placed between a silicon substrate and an overlying metallization layer. While Ti.sub.1-x Al.sub.x N.sub.2 films may be prepared by sputtering, that is a complicated process and is not well controlled in terms of metal stoichiometry, especially for via filling.
A thin film of a multi-metallic compound, such a Ti.sub.1-x Al.sub.x N.sub.2, may be formed by flash vaporization of suitable precursor compounds, followed by deposition of the vapor according to a technique known as metalorganic chemical vapor deposition (MOCVD). In a typical MOCVD process, a heat decomposable metalorganic compound, which is commonly referred to as a "precursor" or "source reagent," is contacted with a substrate which has been heated to a temperature above the decomposition temperature of the precursor. Upon contact with the heated substrate, the precursor decomposes to form metallic species, which are then deposited onto a surface so as to form a metallic film or layer. This heat-induced decomposition process may be referred to as pyrolysis. In one version of the MOCVD process, the pyrolysis of the precursor occurs in the presence of a reactant gas so that a metallic compound is formed and then deposited onto a surface. By using more than one precursor, deposition of multi-metallic alloys and compounds is possible.
The semiconductor manufacturing industry has extensive expertise in the use of MOCVD, and employs this process in many production settings. MOCVD is a particularly advantageous process because it allows for strict control of the thickness of the formed layer, and also because a wide variety of substrate geometries may be coated. One example of a prior art apparatus for performing MOCVD is discussed in U.S. Pat. No. 5,399,379 entitled "Low-Pressure Chemical Deposition Process for Depositing High-Density, Highly-Conformal Titanium Nitride Films of Low Bulk Resistivity."
For many semiconductor manufacturing applications, obtaining and maintaining strict control over the stoichiometry of the deposited metallic or multi-metallic layer is paramount. That is, it is usually very important to deposit a metallic or multi-metallic layer such that the molar (or atomic) ratio of the different metals and/or other elements in the layer corresponds very closely to a predetermined value, or falls within a narrow specified range. The stoichiometry (i.e., numerical ratio of different metals and/or elements to one another) of the deposited layer can be strictly controlled if the precursors are delivered into the deposition chamber in a highly uniform and regulated manner. In other words, it is highly desirable to control the relative amounts of vaporized precursor molecules which are present in the deposition chamber of the MOCVD apparatus. The precursor delivery system is therefore an important component of the MOCVD process.
In one prior art precursor delivery system, one or more bubblers are used to deliver one or more precursors, in vapor form, into the deposition chamber. The bubblers are used in conjunction with a carrier gas stream which serves to dilute and deliver precursors into the deposition chamber. With the use of conventional bubblers, however, the gas phase ratio of different precursors in the deposition chamber tends to vary, especially when the number of precursors (and hence bubblers) is increased. As a result, conventional bubblers are not very effective at providing strict control over the composition of a vapor, and hence the composition of the deposited layer.
Flash vaporization has been described as one approach to achieving a controlled delivery of a precursor into a deposition chamber. See, e.g., U.S. Pat. No. 5,204,314, entitled "Method for Delivering an Involatile Reagent in Vapor Form to a CVD Reactor," and U.S. Pat. No. 5,536,323, entitled "Apparatus for Flash Vaporization Delivery of Reagents." As described in these patents, the delivery of a precursor vapor into the deposition chamber of a CVD apparatus may be accomplished by providing the precursor in a liquid form, either neat or in solution, and flowing the liquid onto a flash vaporization matrix structure which has been preheated to a temperature sufficient to flash vaporize the precursor source material. A carrier gas may optionally be flowed past the flash vaporization matrix structure to form a vapor mixture containing the carrier gas and the flash vaporized precursor or decomposition product(s) thereof. These precursor delivery systems, as described in the aforementioned patents, have addressed many of the problems associated with controlled delivery of precursors into deposition chambers.
Although MOCVD and flash vaporization are known in the art, these processes have not, to date, been effectively used to produce multi-metallic films having metal stoichiometries within tight specifications. Thus, there exists a need for processes that may be used to prepare multi-metallic films. The present invention addresses this need and provides further related advantages as described herein.